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The electric field in metal is zero in electrostatics. But in the Rutherford gold foil experiment, alpha particles get deflected from the gold foil showing the presence of an electric field there. I don't understand this contradiction.

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    $\begingroup$ Because if you get close to a gold nucleus (inside the electron cloud) you sense the charge on the nucleus - it is no longer screened by the electrons. $\endgroup$
    – Jon Custer
    Commented Sep 8, 2021 at 16:46
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    $\begingroup$ net field at macro distances is quite different from local field at atomic distances $\endgroup$ Commented Sep 8, 2021 at 17:02

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The gold foil is overall neutral. That is correct. The nuclei of the gold atoms, like every other atomic nucleus, are positively charged. In Rutherford's gold foil atoms, the gold foils are bombarded with $\alpha$-particles ($He^{2+}$). Most of the $\alpha$ particles pass through the gold foil without any appreciable deflection because of a lot of intra-atomic "free space". A small fraction passes near the gold atoms and gets deflected by large angles. The $\alpha$-particles that collide head-on with the gold nuclei are reflected. Gold is chosen, because it is a heavy metal with a massive nucleus, which also has the convenient property of being very malleable. This helps with making the foil extremely thin (of the width of a thousand atoms).

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  • $\begingroup$ None of your words is an answer to the question. $\endgroup$
    – Swami
    Commented Sep 14, 2021 at 3:29
  • $\begingroup$ @Swami My answer describes what happens at the atomic scale in Rutherford's gold foil experiment. The overall neutrality of the gold foil is explained by the number of protons and electrons being equal. The interactions between the alpha particles and the nuclei arise because there is no screening effect by the electrons near the gold nuclei. $\endgroup$
    – Mechanic
    Commented Sep 14, 2021 at 3:33

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